The present invention relates to a direction indicator of a type for providing compass bearings.
Devices for indicating compass directions are well known in the art. The most widely used of such devices is the magnetic compass. The magnetic compass essentially comprises a magnetic indicator needle mounted to rotate about a vertical axis on a body which has compass directions marked thereon. The indicator needle is mounted in such a way that there is minimal resistance to its rotational movement with respect to the body so that whatever the horizontal orientation of the body the needle will align itself with magnetic North. The compass direction markings on the body may then be aligned so that the marking for North is aligned with the needle pointing towards magnetic North. This may be achieved by rotating the compass body itself or by providing direction markings on a structure itself rotatably mounted on the compass body. Any desired compass bearing can then be obtained from the direction markings. Such devices are effective but tend to be relatively expensive to manufacture if they are to be both robust and accurate, and in any event can only indicate the direction of magnetic North rather than true North.
Alternative methods of determining compass bearings are known which use the bearing of the sun at a known time as a reference. For example a normal analogue watch may be used. This very crude method is based on the fact that when the sun is at its highest point it will be either due North or due South of the observer, depending on the observers location. On a given meridian, this corresponds to 12.00 in the Winter and 13.00 in British Summer time. Thus if the observer is located in the Northern hemisphere the sun will be due South at noon and if the observer is located in the Southern hemisphere the sun will be due North at noon. The method also depends on the fact at any given time the position of the sun is crudely related to the time of day and therefore to the position of the watches hour hand. The exact method used is to first determine the point midway between the point indicated by the hour hand and the position of the midday hour marking. An imaginary line drawn from the centre of the watch face to this midway point is then pointed at the sun. The direction then indicated by a line drawn from the centre of the watch face to the midday hour marking will be roughly North/South (depending on which hemisphere the observer is located in). All other compass bearings can be determined using this as the reference. It will be appreciated that this method is relatively difficult to perform and cannot be used to obtain accurate bearings. Furthermore, this method has the disadvantage that the observer must always have a clear line of sight to the sun whenever a bearing is to be taken.